For the guitars, I'm using a mix of brtstack and hotrod on a digitech GNX-1.

My problem is that instruments tend to get lost in the mix (unable to hear arpeggios and chords, very muddy, no highs etc). The guitars are very midrangey and a bit buzzy, and I think this might be where the problem is coming from. I was wondering if there's anything I can do with the EQ, compressors, or whatever to fix this.

I don't know too much right now (boost mids to cut through, compress vocals, etc), but I can learn pretty fast.

No need to apologize for the meek set up. What you have is more than adequate.

The best advice I could give you is that compressors and EQ should be used only for a desired purpose while recording, rarely should they be used to ''fix" significant problems.

Often when a mix is muddy in the mids, its a result of:
1. Too much compression on voice, guitar, drums, etc.
2. Objects or instruments occupying the same position(s) in the mix (panning)
3. Too much EQing of Vox or guitar

Try keeping the levels in check and avoid Comp / EQ unless you're using it to get a very specific sound.

yes
and adding a different reverb can give the sound a different space

use of hi pass ... and lo pass filters can help sounds not crowd each other

do as much as possible to a mix before using EQ
I find that if you can get a good result with just pan, filters and perhaps some comp
... then when things are much easier when it comes time to get to the details of EQ and automation

Sounds to me when, you say 'buzzy' sound in the guitars, your unhappy with the sound. if so, i'd record them again getting a good sound before hitting the red button. If you wanna stick with the takes you have, then try sweeping through the frequences with a narrow boost untill you hear what you don't like popping out at you even more. then cut some of it out. or you could do the same idea but by cutting the frequences on your sweep of taste.. Eq can be great for getting out of a hole, just don't over use it!

When people say : do as much as you can before eqing .. what exactly does this mean ?

Does this also mean filtering ? and what exactly is the difference ? I know a big topic ...

as of right now, to me , based mostly in the digital domain many of my Eqs and filters have a lot of the same characteristics . For example the Sonakis EQ has a large 24 db cut to it .. which to me seems more like filtering than EQ .. and the Q in Cubase has a lot of boost and sculpting charecteristics ..

So , would something like this be still considered EQ and should i avoid it till the end ? i know it's all relative but ..

or do what people mean is to try and get everything fitting as well as it can in the mix before EQing ?